For a certain crowd longing for FF and lens addicts (I belong to both groups), focal reducers are all the rage.

Yet, I am baffled when I see the reasoning of some people on those. Folks will write : I have a 100mm F2.8 lens, and the focal reducer will turn it into a 71mm, F2 lens.

Hmm, ok, but that's still thinking in APS-C terms and discounting the 1.5 crop factor of our current NEX cameras. Why not reason in FF terms to start with, and just agree that focal reducers roughly negate the 1.5 crop (I said roughly).

If we do the math, a NEX equipped with 0.71 focal reducer, and with a 100/2.8 lens mounted with give a 106/2.9 equivalent in FF terms.

So rather than putting our brains thru torturous calculation it'd be much easier to just think of focal reducers as striking the crop factor. Of course, the shorter the focal range, the more true that is, a 50mm/1.8 becomes a 53/1.9, and a 28/2.8 translates into a 30/2.9. And so on.